Substantial recent research examines the efficacy and biological basis of many types of complementary and alternative (CAM) therapies. However, real-world use of CAM has been largely overlooked, despite calls for CAM therapies to be studied in the manner in which they are practiced and urging high prioritization for research that includes clinical outcomes, cost-effectiveness, and the decision-making process for patients and providers. There is, therefore, heightened need for enriched understandingparticularly given CAMs growing popularity, which fortunately offers stores of new data for research. Recent studies suggest that Americans seek CAM treatments far more often for chronic musculoskeletal pain (CMP) than for any other condition. Among CAM treatments for CMP, acupuncture and chiropractic (A/C) care are among those with the highest acceptance by physician groups and the best evidence to support their use. Further, recent alarming increases in delivery of opioid treatment and surgical interventions for chronic paindespite their high costs, potential adverse effects, and modest efficacy suggests the need to evaluate the outcomes associated with promising non-pharmacological/non-surgical CAM treatments for CMP, which are often well accepted by patients and increasingly used in the community. This application responds to the NCCAM program announcement PAR-08-045, Outcomes, Cost-Effectiveness and the Decision Making Process to Use CAM. This multi-phase, mixed methods study will: (1) conduct an retrospective study using information from electronic medical records (EMRs) of a large HMO to identify unique clusters of patients with CMP (e.g., those with differing demographics, histories of pain condition, use of allopathic and CAM health services, and comorbidity profiles) that may be associated with different propensities for A/C utilization and/or differential outcomes associated with such care; (2) use qualitative interviews to explore allopathic providers recommendations for A/C and patients decisions to pursue and retain CAM care; and (3) prospectively evaluate health services/costs and broader clinical and functional outcomes associated with the receipt of A/C relative to carefully matched comparison participants receiving traditional CMP services. Sensitivity analyses will compare methods relying solely on EMR-derived data versus analyses supplementing EMR data with conventionally collected patient and clinician data. Successful completion of these aggregate aims will provide an evaluation of outcomes associated with the real-world use of A/C services. The trio of retrospective, qualitative, and prospective study will also provide a clearer understanding of the decision-making processes behind the use of A/C for CMP and a transportable methodology that can be applied to other health care settings, CAM treatments, and clinical populations.